1. Field of the Invention
The present invention relates to a data transmission technology. More particularly, the present invention relates to an orthogonal frequency division multiplexing (OFDM) transmitting and receiving method and a device thereof.
2. Description of Related Art
OFDM technology using a concept of parallel data transmission and frequency division multiplexing has been in the 1960s, and has been widely applied to communication system and so on currently. Generally speaking, a communication system performs the transmission in the following two manners, namely single carrier and multi-carrier, under the limitation of constant bandwidth. The “multi-carrier transmission” means that a user can use a plurality of subcarriers at the same time to transmit and receive signals. The basic concept of the OFDM transmission uses a plurality of orthogonal subcarriers to transmit signals which are originally a single batch of high-speed data at a lower transmission speed.
The OFDM technology, having a higher data transmission speed and a characteristic of effectively overcoming frequency selective fading channel, has been widely applied to various wireless communication systems at present.
According to a common OFDM system as shown in FIG. 1A, an inputted complex symbol signal d(k) has a real part d0(k) and an imaginary part d1(k), i.e. d(k)=d0(k)+j·d1(k), where d0(k) and d1(k) are real numbers and k=0, 1, 2, . . . , N−1 representing different subcarriers. Then, an inverse Fourier transform is adopted for modulation, and the data is carried on the subcarrier for transmission in the manner as shown in FIG. 1B. FIG. 1C is a schematic view illustrating an orthogonality of the subcarriers.
Currently, real parts and imaginary parts of signals are carried on cosine and sine subcarriers of a same frequency to transmit and receive data. However, under this architecture, the system performance is hardly to increase and to realize the frequency diversity.
Therefore, for those skilled persons and researchers, how to improve the performance and the frequency diversity without increasing the complexity of the system is a key issue.